Hey there,
Personally I think you'd have more luck just showing your composer what kind of thing you're after. It's all good and well to learn some terminology, but don't expect to be able to use it accurately for a while -- you'll probably just end up confusing your composer.
The best thing you can do is find tracks that represent the flavour of the piece you want. But if you want your composer to really shine - you have to accept that their stylistic choices and ideas will come through alongside that idea (which is really what you want, if you appreciate how good music can really enhance a game, otherwise you just end up with carbon copy stuff that sounds like everything else). Good 'casting' is key here.
The reason trying to describe musical concepts you don't really understand is a bad idea is because we all have different interpretations of things, and unless you really, really know what you're talking about, at some point you're just going to get confused, the composer will get confused, and if they have questions, you'll probably end up sending them in a different direction altogether.
A good composer will be able to pick up on the soundscape/ideas you like based on the music you send them as examples. Just keep in mind that you should be looking for things that represent the feeling or vibe or idea you want, or maybe the sounds -- be careful about getting to caught up in wanting things exactly like the 'temp' track, or the track you had in mind when you wrote the scene/whatever. Of course feel free to describe things you like - just don't feel like you have to be 'musical' about it. You can just pick out the bits of the track you like, describe the sounds you're hearing (maybe you like the sort of continuous low bass stuff, or the eerie synth pads, or the light percussion or whatever - if you can't describe it musically just say what you're hearing, and this is why it's useful to have examples).
Just my opinion.
